Secondary battery and electric device

Abstract

The application provides a secondary battery and a power consumption device. The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on the surface of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material. The positive electrode active material comprises a lithium iron phosphate material doped with an M element and a Q element. The M element comprises one or more of Mn, Ni, Co, Cr, Cu, Bi and Sb, and the Q element comprises one or more of F, N and Cl.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] The improvement of energy density of secondary batteries often comes at the cost of rate performance and cycle stability. How to improve the energy density, rate performance and cycle stability of secondary batteries at the same time is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a secondary battery and an electrical device.

[0005] The first aspect of this application provides a secondary battery, the secondary battery including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on the surface of the positive current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including lithium iron phosphate material doped with M and Q elements, wherein M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0006] The Q element doped in the positive electrode active material can replace the oxygen at the oxygen sites in lithium iron phosphate, causing cell distortion, increasing the cell volume, expanding the lithium-ion migration channels, and improving the rate performance of the secondary battery; the M element doped in the positive electrode has high electronegativity and a strong ability to attract electrons, making Fe... 2+ / Fe 3+ The increased redox potential improves the voltage plateau of the secondary battery, thereby increasing its discharge voltage and energy density. Simultaneous doping of the positive electrode active material with both M and Q elements achieves a simultaneous improvement in the energy density and rate performance of the secondary battery.

[0007] In any embodiment, the composition of the positive electrode active material includes:

[0008] LiFe 1-x M x PO y Q z ,

[0009] Where, 0 < x ≤ 0.1, 3.85 ≤ y ≤ 4, 0 ≤ z ≤ 0.05; M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0010] In any embodiment, M includes Mn; Q includes F.

[0011] The different coordination charges of the anions of element Q and the anions of element O will cause inequivalent substitution, increasing the lattice instability and sacrificing the cycle stability of the secondary battery; when element M includes Mn and element N includes F, Mn doping causes the Jahn-Teller effect to occur during charge and discharge of the positive electrode active material, resulting in two Mn-O bonds being elongated, making P 5+ and F - have a more stable coordination structure, improving the cycle stability of the secondary battery while improving the energy density and fast charging performance of the secondary battery. The Jahn-Teller effect also causes four Mn-O bonds of MnO₆ 2- to be shortened and the Fe-O bond to be elongated, increasing the redox potential of Fe 2+ / Fe 3+ At the same time, the F element at the oxygen site can further increase the strength of the Mn-O-F bond through strong electronegativity, further enhancing the electrochemical potential of the positive electrode active material, and further playing the role of improving the voltage platform and increasing the energy density through the synergistic effect of Mn and F.

[0012] In any embodiment, 0.005 ≤ x ≤ 0.05, 0.001 ≤ z ≤ 0.01.

[0013] When x and y of the positive electrode active material are within the above ranges, the energy density, cycle stability, and rate performance of the secondary battery can be balanced.

[0014] In any embodiment, the positive electrode active material further includes carbon element, and based on the total mass of the positive electrode active material, the mass content of the carbon element is 1.05% - 1.35%.

[0015] The positive electrode active material with a carbon content within the above range has a low powder resistivity, which is beneficial to improving the rate performance of the secondary battery.

[0016] In any embodiment, the unit cell parameters of the positive electrode active material satisfy:

[0017]

[0018] This lithium iron phosphate positive electrode active material has a large unit cell parameter b, which is beneficial to expanding the lithium ion transmission channel and improving the rate performance.

[0019] In any embodiment, the cell volume V of the positive electrode active material is:

[0020] This lithium iron phosphate cathode active material has a large cell volume V, which is beneficial for expanding the lithium-ion transport channels and improving rate performance.

[0021] In any embodiment, the Fe-O bond length L1 of the positive electrode active material satisfies: The PO bond length L2 of the positive electrode active material satisfies: 1.533

[0022]

[0023] This positive electrode active material has a longer Fe-O bond length L1 compared to pure lithium iron phosphate material, which is beneficial to Fe 2 + / Fe 3 The increase in redox potential improves the discharge potential of the positive electrode active material and increases the energy density of the secondary battery.

[0024] In any embodiment, the compacted density of the positive electrode active material powder satisfies: 2.509 g / cm³. 3 -2.571g / cm 3 .

[0025] This positive electrode active material has a high powder compaction density, which is beneficial to further improving the energy density of secondary batteries.

[0026] In any embodiment, the particle size D50 of the positive electrode active material satisfies: 0.79um-1.35um.

[0027] Positive electrode active materials with particle size distribution D50 within the above range have suitable grain size, which is beneficial to the balance between rate performance and energy density of secondary batteries.

[0028] In any embodiment, the discharge capacity of the positive electrode active material at a discharge rate of 0.1C is greater than or equal to 158 mAh / g.

[0029] This positive electrode active material has a high discharge capacity, which is beneficial to improving the energy density of secondary batteries.

[0030] In any embodiment, the discharge voltage of the secondary battery at a discharge rate of 0.1C is 3.396V-4.036V.

[0031] This secondary battery has a high discharge voltage, which is beneficial for further improving the energy density of the secondary battery.

[0032] A second aspect of this application provides an electrical device comprising the secondary battery of the first aspect. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0034] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0035] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0036] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0037] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0038] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

[0039] Explanation of reference numerals in the attached figures:

[0040] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0041] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] Lithium iron phosphate (LFP) materials, as positive electrode active materials, have advantages such as low cost, high safety, and long cycle life; however, pure-phase LFP materials have low electronic conductivity (10⁻⁶). -9 cm·s -1 Low ionic conductivity (10) -13 ~10 - 16 cm 2 ·s -1 The low discharge voltage is a drawback of lithium batteries. Discharge voltage refers to the voltage at which the battery capacity is discharged to a certain level during use. It is usually defined as the voltage at which the battery discharge capacity reaches about 50% of the rated capacity. Low discharge voltage leads to lower energy density in secondary batteries. Low electronic conductivity and low ionic conductivity result in low electron and ion transport speeds in secondary batteries, making it difficult to improve the rate performance of secondary batteries.

[0049] [Positive electrode active material]

[0050] Based on this, this application proposes a positive electrode active material, which comprises lithium iron phosphate material doped with M and Q elements, wherein M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0051] The Q element doped in the positive electrode active material can replace the oxygen at the oxygen sites in lithium iron phosphate, causing cell distortion, increasing the cell volume, expanding the lithium-ion migration channels, and improving the rate performance of the secondary battery; while the M element doped in the positive electrode has high electronegativity and a strong ability to attract electrons, making Fe... 2+ / Fe 3+ The increased redox potential improves the voltage plateau of the secondary battery, thereby increasing its discharge voltage and energy density. Simultaneous doping of the positive electrode active material with both M and Q elements achieves a simultaneous improvement in the energy density and rate performance of the secondary battery.

[0052] In some embodiments, the composition of the positive electrode active material includes:

[0053] LiFe 1-x M x PO y Q z ,

[0054] Among them, 0 < x ≤ 0.1, 3.85 ≤ y ≤ 4, 0 ≤ z ≤ 0.05; M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0055] In some embodiments, x can be selected from one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or the numerical range between any two of them. [[ID=__]]

[0056] In some embodiments, y can be selected from one of 3.85, 3.86, 3.87, 3.88, 3.89, 3.90, 3.91, 3.92, 3.93, 3.94, 3.95, 3.96, 3.97, 3.98, 3.99, 4 or the numerical range between any two of them.

[0057] In some embodiments, z can be selected from one of 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0. and the numerical range between any two of them.

[0058] The composition of the positive electrode active material can be tested by phase analysis methods such as X-ray diffraction method in combination with component analysis methods such as inductively coupled plasma emission spectrometry.

[0059] In some embodiments, M includes Mn; Q includes F.

[0060] The different coordination charges of the anions of Q element and the anions of O element will lead to unequal valence substitution, increasing the instability of the crystal lattice and sacrificing the cycle stability of the secondary battery; when the M element includes Mn and the N element includes F, Mn doping causes the Jahn-Teller effect to occur during the charge and discharge of the positive electrode active material, resulting in two Mn-O bonds being elongated, making the coordination structure of P 5+ and F - more stable. While improving the energy density and fast charging performance of the secondary battery, the cycle stability of the secondary battery is simultaneously improved. The Jahn-Teller effect also shortens the four Mn-O bonds of MnO6 2- and elongates the Fe-O bond, increasing the redox potential of Fe 2+ / Fe 3+ At the same time, the F element at the oxygen site can further increase the strength of the Mn-O-F bond through its strong electronegativity, further enhancing the electrochemical potential of the positive electrode active material, and further playing the role of improving the voltage platform and increasing the energy density through the synergistic effect of Mn and F.

[0061] In some implementations, 0.005 ≤ x ≤ 0.05, 0.001 ≤ z ≤ 0.01.

[0062] The x and y values ​​of the positive electrode active material, within the above range, can balance the energy density, cycle stability, and rate performance of the secondary battery.

[0063] In some embodiments, the positive electrode active material further includes carbon, with a carbon content of 1.05%-1.35% based on the total mass of the positive electrode active material.

[0064] In some embodiments, the carbon content, based on the total mass of the positive electrode active material, can be selected as 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, or any value range between the two.

[0065] Based on the total mass of the positive electrode active material, the carbon content can be tested using any method known in the art. As an example, the carbon content is tested by infrared absorption after combustion in a high-frequency induction furnace. The specific testing procedure follows the standard GB / T20123-2006 / ISO 15350:2000 "Determination of Total Carbon and Sulfur Content in Iron and Steel - Infrared Absorption Method After Combustion in a High-Frequency Induction Furnace". A carbon-sulfur analyzer, such as the DEK HCS infrared carbon-sulfur analyzer, is used for convenient measurement.

[0066] Positive electrode active materials with carbon content within the above range have lower powder resistivity, which is beneficial to improving the rate performance of secondary batteries.

[0067] In some embodiments, the cell parameters of the positive electrode active material satisfy:

[0068]

[0069] In some implementations, a can be selected as

[0070]

[0071] The range of values ​​for any one of them or between any two of them.

[0072] In some implementations, b can be selected as

[0073] The range of values ​​for any one of them or between any two of them.

[0074] In some implementations, c can be selected as The range of values ​​for any one of them or between any two of them.

[0075] LiFePO4 has an olivine-type structure and belongs to the orthorhombic crystal system, space group Pnma. Each unit cell contains four LiFePO4 units. In the LiFePO4 crystal structure, O atoms are arranged in a slightly distorted hexagonal close-packed configuration, phosphorus atoms are located at the 4c ​​position of the oxygen tetrahedron, and Fe and Li atoms are located at the 4c ​​and 4a positions of the oxygen octahedron, respectively. FeO6 octahedra are connected by common points on the bc plane. One FeO6 octahedron shares an edge with two LiO6 octahedra and one PO4 tetrahedron. + A continuous straight chain with shared angles or edges is formed at position 4a. The Li+ parallel to the c-axis is a continuous straight chain, which can form a two-dimensional diffusion motion along the c-axis, freely detaching or embedding.

[0076] Cell parameters refer to the length of the smallest repeating unit in the a, b, and c directions of a crystal. They can be tested using any method known in the art. For example, they can be tested and calculated using X-ray diffraction. Specifically, the Xpert PRO X-ray powder diffractometer from the United States is used for testing, and the EXPGUI software is used for calculation.

[0077] This lithium iron phosphate cathode active material has a large cell parameter b, which is beneficial for expanding the lithium-ion transport channels and improving rate performance.

[0078] In some embodiments, the cell volume of the positive electrode active material is 290.718.

[0079]

[0080] In some embodiments, the cell volume of the positive electrode active material can be selected as follows:

[0081] The range of values ​​for any one of them or between any two of them.

[0082] The cell volume of a positive electrode active material refers to the size of the cell determined by its cell parameters. It can be tested by any method known in the art. For example, it can be tested by X-ray diffraction and calculated by EXPGUI software.

[0083] This lithium iron phosphate cathode active material has a large cell volume V, which is beneficial for expanding the lithium-ion transport channels and improving rate performance.

[0084] In some embodiments, the Fe-O bond length L1 of the positive electrode active material satisfies: The PO bond length L2 of the positive electrode active material satisfies: 1.533

[0085]

[0086] In some embodiments, the Fe-O bond length L1 of the positive electrode active material can be selected as...

[0087] Or the range of values ​​between any two.

[0088] In some embodiments, the PO bond length L2 of the positive electrode active material satisfies: 1.533

[0089]

[0090] Or the range of values ​​between any two.

[0091] The Fe-O bond length L1 and PO bond length L2 of the positive electrode active material can be tested by any method known in the art. For example, they can be tested by X-ray diffraction and calculated by EXPGUI software.

[0092] This positive electrode active material has a longer Fe-O bond length L1 compared to pure lithium iron phosphate material, which is beneficial to Fe 2+ / Fe 3+ The increase in redox potential improves the discharge potential of the positive electrode active material and increases the energy density of the secondary battery.

[0093] In some embodiments, the compacted density of the positive electrode active material under a pressure of 3t satisfies the following condition: 2.509 g / cm³. 3 -2.571g / cm 3 .

[0094] The compaction density of the positive electrode active material powder under a pressure of 3t can be tested using any method known in the art. As an example, 1g of the positive electrode active material is weighed and added to a cylindrical mold with a circular hole of cross-sectional area S. A pressure of 3t is applied to the powder inside the mold and held for 30s, and the powder thickness is recorded as t. The compaction density ρ of the positive electrode active material powder can then be calculated using the following formula: ρ=m / (S×t).

[0095] In some embodiments, the compaction density of the positive electrode active material under a pressure of 3t can be selected as 2.509 g / cm³. 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3 2.54 g / cm 3 2.55g / cm 3 2.56 g / cm3 2.571 g / cm 3 Or the range of values ​​between any two.

[0096] This positive electrode active material has a high powder compaction density, which is beneficial to further improving the energy density of secondary batteries.

[0097] In some embodiments, the particle size D50 of the positive electrode active material satisfies: 0.79um-1.35um.

[0098] D50 refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% for the positive electrode active material, and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0099] In some embodiments, the particle size D50 of the positive electrode active material can be selected as 0.79 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1.0 μm, 1.05 μm, 1.1 μm, 1.15 μm, 1.16 μm, 1.17 μm, 1.18 μm, 1.19 μm, 1.2 μm, 1.21 μm, 1.22 μm, 1.23 μm, 1.24 μm, 1.25 μm, 1.3 μm, 1.35 μm, or any value range between the two.

[0100] Positive electrode active materials with particle size distribution D50 within the above range have suitable grain size, which is beneficial to the balance between rate performance and energy density of secondary batteries.

[0101] In some embodiments, the discharge capacity of the positive electrode active material at a discharge rate of 0.1C is greater than or equal to 158 mAh / g.

[0102] The specific capacity of the positive electrode active material at a discharge rate of 0.1C can be tested using methods known in the art. As an example, the secondary battery is placed in a 25°C oven and left to stand for 2 hours, followed by a charge-discharge test. One charge-discharge process is as follows: the battery is charged at a constant current of 0.1C to 3.65V, then charged at a constant voltage until the charging current is less than 0.05C; this is paused for 5 minutes; the battery is then discharged at a constant current of 0.1C to 2.0V; this is paused for another 5 minutes. The specific capacity of the positive electrode active material at a discharge rate of 0.1C is calculated by dividing the capacity released by the secondary battery from a full charge (3.65V) to a full discharge (2.0V) by the mass of the positive electrode active material.

[0103] In some embodiments, the discharge specific capacity of the positive electrode active material at a discharge rate of 0.1C can be selected as 158mAh / g, 158.5mAh / g, 159mAh / g, 159.5mAh / g, 160mAh / g, 160.5mAh / g, 161mAh / g, 161.5mAh / g, 162mAh / g, or any value range between the two.

[0104] This positive electrode active material has a high discharge capacity, which is beneficial to improving the energy density of secondary batteries.

[0105] In some implementations, the discharge voltage of the secondary battery at a discharge rate of 0.1C is 3.396V-4.036V.

[0106] The discharge voltage of a secondary battery at a discharge rate of 0.1C can be tested using any method known in the art. As an example, the secondary battery is placed in a 25°C oven and left to stand for 2 hours, followed by a charge-discharge test. The charge-discharge process is as follows: constant current charging at 0.1C to 3.65V, then constant voltage charging continues until the charging current is less than 0.05C, at which point the charging is stopped; a 5-minute pause is performed; constant current discharge at 0.1C to 2.0V is performed; a 5-minute pause is also performed. The discharge voltage is taken as the voltage at which the specific capacity is 70 mAh / g.

[0107] In some embodiments, the discharge voltage of the secondary battery at a 0.1C discharge rate can be selected from 3.396V, 3.398V, 3.400V, 3.402V, 3.404V, 3.406V, 3.408V, 3.41V, 3.412V, 3.414V, 3.416V, 3.418V, 3.42V, 3.43V, 3.44V, 3.45V, 3.46V, 3.47V, 3.48V, 3.5V, 3.6V, 3.7V, 3.8V, 3.9V, 4.0V, 4.01V, 4.02V, 4.03V, 4.036V, or any value range between the two.

[0108] This secondary battery has a high discharge voltage, which is beneficial for further improving the energy density of the secondary battery.

[0109] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0110] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0111] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0113] [Negative electrode plate]

[0114] In some embodiments, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0115] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0116] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0117] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0118] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0119] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0121] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0122] [Electrolytes]

[0123] In some embodiments, the secondary battery also includes an electrolyte. The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid-state.

[0124] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0125] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0126] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0127] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0128] [Isolation membrane]

[0129] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0130] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0131] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0132] A third aspect of this application provides an electrical device comprising a secondary battery as described in the second aspect.

[0133] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0134] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0135] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0136] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0137] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0138] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0139] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0140] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0141] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0142] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0143] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0144] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0145] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0146] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0147] Example

[0148] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0149] Example 1

[0150] (1) Preparation of positive electrode active material

[0151] The raw materials are iron phosphate, lithium carbonate, manganese nitrate, carbon source, and lithium fluoride, and are added in the proportion and order that the finished product has the molecular formula of lithium iron phosphate. The carbon source is glucose, sucrose, and polyethylene glycol (PEG) with a weight average molecular weight of 2000-4000.

[0152] Raw materials are added to solvent water in sequence and wet-milled to obtain a mixed slurry. The mixed slurry is spray-dried, and the dried product is then placed in a roller furnace and sintered at 750°C in the absence of air for 28 hours. After natural cooling to a material temperature of less than 80°C, the material is discharged to obtain calcined material. The calcined material is then crushed, sieved, and demagnetized to obtain the positive electrode active material.

[0153] (2) Preparation of positive electrode sheet

[0154] The above-mentioned positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black were mixed in a mass ratio of 96.5:2.0:1.5, and then N-methylpyrrolidone (NMP) solvent was added to form a uniform positive electrode slurry. This slurry was coated onto a carbon-coated aluminum foil with a thickness of 13 μm and a coating density of 26 mg / cm2. After drying, cold pressing, and slitting, the positive electrode sheet of this application was obtained.

[0155] (3) Preparation of negative electrode sheet

[0156] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1. Deionized water is added, and the mixture is stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil with a thickness of 8 μm. After drying, it is cold-pressed and slit to obtain a negative electrode sheet.

[0157] (4) Separating membrane

[0158] A 12μm thick polypropylene separator membrane was selected.

[0159] (5) Electrolyte

[0160] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a mass ratio of 30:70. LiPF6 was added and dissolved completely. Then, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added and mixed evenly to obtain an electrolyte with a LiPF6 concentration of 1 mol / L and a mass content of 3% for both VC and FEC.

[0161] (6) Assembly of secondary batteries

[0162] The positive and negative electrode sheets are baked in a 110°C high-temperature oven for 7 hours to remove moisture. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator acting as a separator between the positive and negative electrode sheets. After being wound into a square bare cell, it is placed in an aluminum-plastic film, injected with the appropriate non-aqueous electrolyte, and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a lithium-ion battery is obtained.

[0163] The secondary batteries in Examples 2-7 and Comparative Examples 1-4 are prepared in a similar manner to the secondary battery in Example 1. The difference lies in the adjustment of the input ratio of manganese source and fluorine source during the preparation of the positive electrode active material, which results in an adjustment of the molar ratio of manganese, fluorine and lithium in the final product. The specific product parameters are shown in Table 1.

[0164] In Example 3 and Comparative Example 3, nickel nitrate, a nickel source, was also added during the feeding stage.

[0165] The preparation method of Example 7 is basically the same as that of Example 1, except that the sintering temperature is adjusted to 770℃.

[0166] Table 1

[0167]

[0168]

[0169] II. Battery Performance Testing

[0170] 1.0.1C Battery Specific Capacity Test Method

[0171] The lithium-ion battery was placed in a 25°C oven and left to stand for 2 hours before a charge-discharge test was performed. One charge-discharge cycle was as follows: The battery was charged at a constant current of 0.1C to 3.65V, then charged at a constant voltage until the charging current was less than 0.05C; this was paused for 5 minutes; the battery was then discharged at a constant current of 0.1C to 2.0V; this was paused for another 5 minutes. This constitutes one charge-discharge cycle of the battery.

[0172] Battery capacity = Discharge capacity of secondary battery / Mass of positive electrode active material.

[0173] 2. Discharge voltage test

[0174] The lithium-ion batteries of the examples and comparative examples were placed in a 25°C oven and left to stand for 2 hours before being subjected to charge-discharge tests. One charge-discharge process was as follows: constant current charging at 0.1C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; a 5-minute pause was then performed; constant current discharging at 0.1C to 2.0V was then performed; a 5-minute pause was also performed. The discharge voltage was taken as the discharge voltage when the specific capacity was 70 mAh / g.

[0175] 3. Energy density test

[0176] The lithium-ion battery was placed in a 25℃ oven and left to stand for 2 hours before undergoing a charge-discharge test. One charge-discharge cycle was as follows: constant current charging at 1C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; a 5-minute pause was then performed; constant current discharging at 1C to 2.0V was then performed; a 5-minute pause was also performed. This constitutes one charge-discharge cycle of the battery.

[0177] Cell mass energy density (Wh / kg) = (capacity of the third discharge during the cycle × discharge plateau) / mass of positive electrode active material.

[0178] 4. Cyclic stability test

[0179] The lithium-ion battery was placed in a 60℃ oven and left to stand for 2 hours before undergoing charge-discharge testing. One charge-discharge cycle was as follows: constant current charging at 1C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; a 5-minute pause; constant current discharging at 1C to 2.5V; a 5-minute pause. This constituted one charge-discharge cycle. This process was repeated continuously for 2000 cycles. The ratio of the battery's discharge capacity to the initial discharge capacity was calculated as the cycle capacity retention rate.

[0180] 5. Ratio Performance Test

[0181] The lithium-ion battery was placed in a 25°C oven and left to stand for 3 minutes before being subjected to charge-discharge tests. The charge-discharge process was as follows: constant current charging at 0.1C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; paused for 5 minutes; constant current discharging at 0.1C to 2.0V; paused for 5 minutes, and the discharge capacity was recorded as C1; subsequently, the charge-discharge rates were adjusted to 1C, 5C, and 10C, and the discharge capacity at 1C was recorded as C2, and the discharge capacity at 10C as C3. C2 / C1 characterizes the rate performance of the battery at a 1C discharge rate, and C3 / C1 characterizes the rate performance of the battery at a 10C discharge rate.

[0182] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0183] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 2 below.

[0184] Table 2

[0185]

[0186] Table 3

[0187]

[0188] XRD test results show that the positive electrode active material in this application is a lithium iron phosphate phase with an olivine structure. The positive electrode active material in the examples is simultaneously doped with M and Q elements, where M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl. Compared with the material in the comparative example, the positive electrode active material in the examples has a larger cell volume, Fe-O bond length L1, and powder compaction density, which is beneficial to the simultaneous improvement of discharge voltage, energy density, and rate performance of the secondary battery.

[0189] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on the surface of the positive current collector, the positive electrode film layer includes a positive electrode active material, and the composition of the positive electrode active material includes: LiFe 1-x M x PO y Q z , Wherein, 0.03≤x≤0.05, 3.85≤y≤4, 0.0005≤z≤0.005; M includes one or more of Mn, Ni, Co, Cr, and Cu, and Q includes one or more of F and Cl.

2. The secondary battery according to claim 1, characterized in that, M includes Mn; Q includes F.

3. The secondary battery according to claim 1, characterized in that, The positive electrode active material also includes carbon, and the mass content of carbon is 1.05%-1.35% based on the total mass of the positive electrode active material.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The positive electrode active material satisfies at least one of the following conditions: (1) The cell parameters of the positive electrode active material satisfy: 10.324Å≤a≤10.343Å, 6.005Å≤b≤6.089Å, 4.689Å≤c≤4.69Å; (2) The cell volume V of the positive electrode active material is 290.718 Å. 3 -292.168Å 3 ; (3) The Fe-O bond length L1 of the positive electrode active material satisfies: 2.080Å≤L1≤2.095Å, and the PO bond length L2 of the positive electrode active material satisfies: 1.533Å≤L2≤1.586Å.

5. The secondary battery according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: (1) The compacted density of the positive electrode active material powder satisfies: 2.509 g / cm³ 3 -2.571g / cm 3 ; (2) The particle size D50 of the positive electrode active material satisfies: 0.79μm-1.35μm; (3) The discharge capacity of the positive electrode active material at a discharge rate of 0.1C is greater than or equal to 158mAh / g.

6. The secondary battery according to claim 1, characterized in that, The secondary battery has a discharge voltage of 3.396V-4.036V at a discharge rate of 0.1C.

7. An electrical device, characterized in that, The electrical device includes the secondary battery as described in any one of claims 1 to 6.

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